Heart failure (HF) is an increasingly prevalent disease that occurs when the cardiac muscle is unable to maintain a sufficient cardiac output. HF patients experience increased morbidity and mortality with death resulting from progressive failure of cardiac mechanical function (pump failure) or ventricular arrhythmias. Pathological structural remodeling of the heart associated with myocyte hypertrophy and/or death is a common feature of HF. Altered Ca release from the sarcoplasmic reticulum (SR) due to deregulated cardiac ryanodine receptor (RyR2) function (i.e. leaky RyR2s) has been implicated in both contractile dysfunction and arrhythmias in HF as well as in the structural remodeling of the failing heart. Indeed, dysregulated RyR2s contribute to HF, and RyR2s are increasingly dysregulated during HF. During HF, autonomic nervous system balance shifts such that there is parasympathetic withdrawal and sympathetic excess. The role of the excess sympathetic nervous system signaling as a mediator of RyR2 dysfunction is clearly established. However, the potential role of the parasympathetic nervous system as a mediator of RyR2 function and dysfunction is unclear. Investigations with vagal (parasympathetic) stimulation have shown promise in treating HF. However the mechanisms for potential benefit of augmenting vagal stimulation to the heart are unknown. The main goal of this proposal is to define the consequences and the underlying mechanisms of parasympathetic stimulation in normal and failing hearts as well as the factors that underlie the beneficial effects of parasympathetic augmentation/vagal stimulation in HF. We propose to 1) Define the role and mechanisms of ventricular Ca cycling modulation by the parasympathetic nervous system; and 2) Determine the modes and mechanisms of muscarinic modulation of myocyte Ca handling in the failing heart and test the therapeutic potential of improved Ca handling via parasympathetic augmentation in HF. A combination of genetic and pharmacologic approaches will be used, in addition to a pre-clinical validated HF model. We propose a systematic integrated approach using a combination of advanced and state-of-the-art biochemical (e.g. protein phosphorylation), cell physiology (multicompartment and high resolution 2D Ca imaging) and biophysical methods (single RyR2 recordings). Information gained will provide mechanistic information that could be used in the optimization of strategies to improve cardiac function through manipulation of the parasympathetic nervous system.